This animation shows the development of the blood vessel associated with the kidneys using the classical "ladder theory" that has been recently disproven as the mesonephric arteries are completely eliminated before metanephric development.[1]

Classical ladder theory - "the mesonephric arteries have a segmental arrangement and persist after regression of the mesonephros, with some of these vessels becoming definitive renal arteries. To avoid interruption of blood flow, such a vascular switching would require an intermediate stage in which two or more segmental mesonephric arteries are connected to a definitive renal artery."